Aperture meter



Dec. 5, 1950 w, E CLARK v APERTURE METER Filed Oct. 1l, 1949 I N VEN TOR.

ATTE] R N EYB Patented Dec. 5, 1950 UNITED STATES `Pirrlaznr oFFlcE APERTURE METER William 4Eugene Clark, Arkansas City, Kans.

Application October 11, 1949, Serial No. 120,683

This invention relates to photographic equipment, and more particularly to a mechanical device for computing camera lens aperture when the other factors or variables are known.

The object of the invention is to provide a device for computing the value of the required lens aperture when the film speed, shutter speed and light intensity are known, or conversely, the device can be used for determining the required value of any of these four variables when the other three are known.

Another object of the invention is to provide a computing device which includes a plurality of coacting, movable, calibrated scales which may be arranged as rings, discs or in the form of a slide rule, and wherein certain of these scales are adapted to be mechanically or operatively connected to the camera shutter adjustment and to the aperture adjustment whereby upon proper setting of the scale, the shutter speed and aperture will be automatically adjusted to their correct positions.

A further object of the invention is to provide a computing device which is adapted to be readily attached to ordinary cameras, the computing device being simple and inexpensive to manufacture.

Other objects and advantages will be apparent during the course of the following description.

In the accompanying drawings forming a part of this application, and in which like numerals are used to designate like parts throughout the same:

Figure 1 is an elevational View showing one form of the computing device;

Figure 2 is an elevational view of a modified computing device.

Referring in detail to Figure 1 of the drawings, the numeral I designates a first ring which has a scale Il of calibrated values of lens aperture thereon. Arranged in spaced concentric relation about the ring I is a ring I2, and the ring I2 is provided with a scale I3 which includes calibrated values of shutter speed.

Movably mounted between the rings III and I2 is a ring I4. The ring I4 is provided with a pair of scales thereon. Thus, the ring I4 includes a scale I5 of calibrated iilm speed values, and the ring I4 also includes a scale I6 of calibrated light intensity values.

A pointer I'I is movably mounted between the rings I2 and I4, and a second pointer I8 is movably mounted between the rings IIJ and I4,

In using the device of Figure 1, the required lens aperture Of the camera can be determined.

1 claim. (c1. zassim when the value of the shutter speed, lightintensity and lm speed are known. Thus,'as` suming that the shutter speed is 1/50 of a second, the light intensity is 4, and the lm speed is 25. Then, the pointer I'I is moved until it coincides with the number 50 on the scale I3; next, the ring I4 is rotated until the number 4 on the light-intensity scale coincides with the pointer Il. Then, the pointer I8 is moved so that one of its ends coincides with the number 25 on the film-speed scale I3 and then the other end of the pointer I8 will coincide with the number 8 on the scale II, and the number 8 is the required value of the lens aperture.

Referring to Figure 2 of the drawings, there is shown a modiiied photographic computing device which includes a body member I9 that is provided with a recess or channel 22 therein. Arranged on one side of the body member I9 is an indicating mark 20, while arranged on the other side of the body member I9 is a scale 2I which includes calibrated values of camera shutter speed.

Arranged for sliding movement in the recess 22 is a plurality of slides having scales and marks thereon. Thus, there is provided a iirst slide 23 which has a scale 24 thereon. The scale 24 includes calibrated values of light intensity. The slide 23 is also provided with an indicating mark 25 thereon.

Arranged adjacent the slide 23 and movably mounted in the recess 22 is a slide 26 which is provided with a scale 2'I thereon. The scale 2l includes calibrated values of iilm speed. The slide 26 is also provided with an indicating mark 28 thereon. Finally, movably mounted in the recess 22 and arranged adjacent the slide 26 is a slide 29 which has a scale 30 of calibrated aperture values thereon. The slide 29 is also provided with an indicating marker 3 I.

The device of Figure 2 can also be used to determine the required value of the lens aperture; when the value of the shutter speed, light intensity and film speed are known. Thus, as;

shown in Figure 2, the slide 23 is moved until its.

mark 25 coincides with the proper value on the shutter speed scale 2l. Then, the slide 26 is4 moved until its mark 23 coincides with the propervalue on the light-intensity scale '24. Next, the slide 29 is adjusted or moved so that its mark 3l coincides with the correct lm speed value on the scale 2l, and finally, the mark 20 will coincide with the required aperture value as shown on scale 30.

From the foregoing it is apparent that a simassasea pyramid elect'is produced. It is toV be under-v stood that the shutter speed value can also be determined by knowing the value of the other three variables. g with either slides, discs or rings. Y Further, the

device shown in Figure 1 is espeeialllyadaptdlto* The device can be constructed-.f

be installed on conventional `amerasgand...such-A 1 device canV be installed at the factory as` the cameras are manufactured.

What is claimed is:

Asca'. newA article:y of' manufacture; a: phatofgraphicfcomputingdevice comprising afxrsttcedr. ring having a scalezof caliizvratedfilensY aperture values; thereon', a secondxe; ring arranged-in' spac'i'edA concentric. relation. about: saixiif'rst ring.'

andv )gia-vingV ai. scale; 'ofz calibrated sl'nitter'-speed:-` values, arthird ring movably .mounted between:

4 said first and said second rings, said third ring having a scale of calibrated light intensity values and a scale of calibrated lm speed values thereon, a rst pointer positioned between said rst and third rings, and a second pointer positioned between said second and third rings said pointers being movable between peripheries of said rings, said first pointer coacting with the scales on said rst and third rings, and said second pointer cooperating; withA the scales=`on said A'second and thirdlrings.

W'ILLIAM EUGENE CLARK.

Y REFERENCES CITED tThe following; references are of record in the l'e" of 'this patent:

' UNITED'- STATES PATENTS 

